The present invention is drawn to a device used to feed molten metal to caterpillar track molds during strip casting.
Casting machines with caterpillar track molds have been developed for the continuous strip casting of aluminum and other metals, the mold being formed by a double row of mold halves which make up two endless moving belts. At the end at which molten metal is fed to the mold the facing mold halves unite and move in this fashion over a certain distance over which they form the actual caterpillar track mold. The mold halves then separate and in a short time meet again at the metal inlet end.
Casting in caterpillar track type molds has been known in the art for some time. (E. Herrmann, Handbuch des Stranggiessens, Dusseldorf 1958, p. 51 ff.).
In the case of casting machines with caterpillar type molds for casting relatively thin strip e.g. 20 mm thick and less, the nozzle for the supply of liquid metal is the most sensitive component. This is mainly due to the fact that there are few materials which can withstand the high temperatures of the hot metal flowing through this part. When the metal being cast is aluminum or an aluminum alloy the nozzle must withstand erosion or dissolution by the metal.
Nozzles for metal feeding have been developed and typical nozzles are described in the U.S. Pat. No. 2,752,649 and the Swiss Pat. No. 508,433 and in the Handbuch des Stranggiessens, pages 60 and 61. The parts of the nozzle which come into contact with the liquid metal are made of a refractory material made up of a mixture of 30% diatomaceous earth (almost pure silica in the form of microscopic cells), 30% asbestos fibres, 20% sodium silicate (dry weight) and 20% lime (to form calcium silicate). Such materials are commercially available under the trade names "Marinite" and "Marimet".
The nozzle described in U.S. Pat. No. 2,752,649 is intended for casting relatively thick aluminum sections which are rectangular in cross section. The mouth of the nozzle features a central front part which runs perpendicular to the axis of the hollow mold space and two sides set back at an angle. The main route for the molten metal in the nozzle branches off at the mouth in such a manner that in practice a stream of metal is directed at an angle against each of the narrow sides of the space in the mold and another stream is directed forwards. As a result, the metal solidifies from the narrow sides towards the middle and the central stream of metal fills the shrinkage gap which forms as the metal solidifies.
This known type of nozzle can not be used for casting relatively thin, wide strips (e.g. 700 to 1500 mm wide and larger, and about 20 mm thick). In addition, the shape of the nozzle mouth is of no use in casting thin, wide strips.
For such a case the same applicant has already developed a nozzle which is provided with inserts of a self lubricating material near the outer edge of the mouthpiece around its whole circumference. These inserts project so far over the surface of the mouthpiece that they prevent any direct contact of the nozzle surface with the mold halves and prevent liquid metal from penetrating the space caused by the play between the mouthpiece and the mold halves.
Although the above mentioned nozzles are made of refractory material and exhibit good thermal insulation and low heat capacity, there is a basic disadvantage in that the material used is not very homogeneous in terms of chemical composition and mechanical properties. It absorbs moisture and is subject to irreversible changes in chemical composition on heating to operating temperature and is thus susceptible to an associated embrittlement or low mechanical strength which, as a rule, allows the nozzle to be used only once.
In spite of the above mentioned low heat capacity and poor thermal conductivity of the known ceramic materials the nozzle must be pre-heated before casting in order to prevent the metal from freezing prematurely at the start of casting.
The object of the present invention is to construct a device for feeding the melt during strip casting in caterpillar track type molds. A further object is to make the device out of a material which will allow the said device to be used repeatedly.